Transmit-receive switch



Oct. 6, 1953 Z RK 2,654,834

TRANSMIT-RECEIVE SWITCH Y Filed Nov. 1, 1949 FIG. I

TRANSMITTER RECEIVER POWER AMP.

R.'F. AME

TRANSMITTER POWER AMP. INVENTOR.

BERT ZARKY Patented Oct. 6, 1953 TRANSMIT-RECEIVE SWITCH Bert Zarky, Chicago, Ill., assignor to Motorola, Inc., Chicago, 111., a corporation of Illinois Application November 1, 1949, Serial No. 124,895

2 Claims.

This invention relates to radio communication apparatus, and particularly to low-power, highfrequency, transmitter-receivers.

Where a radio transmitter and a radio receiver utilize the same antenna, provision usually is made for isolating the receiver from the transmitter during the periods of transmission, in order to protect the receiver from damage and to prevent the receiver from dissipating the power of the transmitter. In most cases relays operated by push-to-talk switches have been used for this purpose. Automatic devices of various kinds such as spark gaps and gaseous discharge tubes have been proposed heretofore to uncouple the receiver from the antenna when the transmitter is operating. These devices have not been adapted for use in low-power, highirequency sets because they consume more power than the sets can afford to expend, particularly at the higher frequencies.

An object of the present invention is to provide an improved automatic transmit-receive switching device that does not require any appreciable power for its operation and which can be employed in low-power, high-frequency sets such as portable, battery-operated, transmitter-receivers.

A further object is to provide an improved transmit-receive switch that does not employ any moving parts nor any discharge means, such as a spark gap or a gas tube, which consumes a substantial amount of power.

A still further object is toprovide novel means in a transmitter-receiver for automatically isolating the receiver from the transmitter whenever the signal fed to the input stage of the receiver rises above a certain low value, such as 1.5 volts.

A feature of the invention is the provision of an improved transmit-receive switch comprising a biased metallic-oxide rectifier (such as a germanium crystal) which affords a high impedance for low-level signals'and a very low impedance for high-level signals (above 1.5 volts, for example).

Another feature is the provision of a novel receiver decoupling means using a metallic-oxide rectifier that consumes negligible powereven at high frequencies.

The foregoing and other objects and features of the inventionwill be apparent from a study of the following description taken in connection with the accompanying drawing, wherein:

Fig. 1 is a schematic view illustrating a portion of a transmitter-receiver utilizing one embodiment of the invention; and.

during transmissions periods.

end of a receiver tuning coil [4. a transmitter tuning coil 44 are inductively cou- 2 Fig. 2 is a schematic view illustrating a modified form of the invention.

In practicing the invention, a suitable metallicoxide rectifier, such as a germanium crystal, is

arranged in the input circuit of the receiver section of a transmitter-receiver. The rectifier, in series with a source of biasing voltage, is connected to the antenna couplin network in such fashion as to prevent any coupling between transmitter and receiver when a very strong signal is impressed upon this network, but the coupling is not affected if weaker signals are picked up.

Hence, all incoming signals (that is, signals picked up from space by the antenna) are fed with only slight attenuation to the receiver R. F. amplifier. Very strong signal voltages will be impressed upon the antenna coupling network The rectifier becomes conductive whenever the voltage impressed upon it exceeds the bias voltage, and when the rectifier conducts, the receiver R. F. amplifier is isolated or uncoupled from the antenna and from the transmitter. In this way the rectifier serves as a transmit-receive switch to prevent the receiver from loading the transmitter during transmission periods.

Fig. 1 shows one way in which the germaniumoxide rectifier ID or other suitable metallic-oxide rectifier is arranged in the input circuit of a receiver.

The positive terminal of the rectifier It is connected to a conductor l2 that leads to one The coil I4 and pled to the antenna 20 by a link coil 16 which provides appropriate transformation ratios for The coil I6 is The conductor I2 is coupled through a blocking capacitor 22 to the control grid 24 of an amplifier tube 25 in the radio-frequency amplifier stage of the receiver. tube 26 is connected to ground, as indicated, and a grid coupling resistor 30 isconnected between the control grid 24 and ground.

The filamentary cathode 28 of the One end of the receiver tuning coil [4 is connected to the conductor I2, as, previously mentioned, and the other end of the coil I4 is grounded as shown. The negative terminal of the rectifier I0 is connected by a conductor 32 to the positive terminal of a bias-voltage source 34 that is grounded on its negative side.

A bypass capacitor 36 between the conductor 32 and ground affords a path for high-frequency currents. The rectifier III, in series with the biasvoltage source 34, shunts the inductor M. The voltage furnished by the biasing source 34 is selected to be of such a value that the rectifier I is nonconductive for all input signals below a certain level, for example, 1.5 volts. This allows signals picked up by the antenna as from space to pass with only slight attenuation to the control grid 24 of the receiver R. F. amplifier.

The transmitter power amplifier includes an amplifier tube 38 having a plate 40 which is connected to a source of plate voltage 42 through the tuning coil 44 and a choke 46. A bypass capacitor 48 shunts the choke 46 and the power supply 42 for high-frequency currents. The

filamentary cathode 50 of the :tube 38is grounded as shown. Normally the receiver R. F. amplifier and the transmitter power amplifier are critically coupled to each other through the medium .be damaged by the strong signal coming from the transmitter. The germanium rectifier It prevents this by becoming electrically conductive when the signal voltagein the coil [4 rises above a certain value,-such as 1.5 volts. -VVhen conducting, the rectifier H] has a resistance of around ZOO-ohmses-compared with a resistance of about-a megoh-m whenit is nonconductive. The capacitance of-the-rectifier I0 is very small so that it acts substantially asa pure resistance.

The receiver-R. F. amplifieris-critically coupled to the transmitter power amplifierwhen the rectifier 1-0 is =nonconductive, However, when the signallevel rises'above the predetermined maximum value (1.5 volts) and the rectifier 10 becomes -conductive,- the low-resistance 'shunt which the rectifier Ill-places across the input coil [4 greatly reduces the circuit Q; This uncouples or isolates-the receiver R. F. amplifier from the transmitter power ampli-fierand from the antenna 20. VVhenthe transmission ceases, the signal .-leve1-drops and the rectifier again becomes nonconductive, thereby restoring the circuit Q to its normal value and coupling the receiver.R.-F. amplifier tdtheantenna 2n-again, so that signals picked up byr-the antenna- 'from space may be received. In this way, the

rectifier 59 serves asan automatic-transmitreceive switch for.alternately coupling the receiverto the antenna 7 during reception periods and uncoupling the receiver from the antenna during transmission periods.

Fig. 2 illustrates-a portiouof "a transmitterreceiver system 'similar to -that shown in --Fig. 1, except that the receiver R. F. amplifier'is coupled by the capacitor-$4 to the coil 44 in the plate circuit of-thetransmitter-power -amplifier. The coils -|4 and 44-, in this instance, are IIOtvlIldllCtiVBl-Y coupled to each 'other. The antenna link coil leis inductively-coupled to the transmitter coil 44 but not to the receiver coil I 4- (being indirectlycoupledto the coil I4 throughthe medium oi the coil 44 and the couplingicapacitor .54). The coupling between .receiver and'transmi'tter', as beforeds critical when the rectifier Ill is nonconductive and is substantially non-existent when *the rectifier I 0 conducts during transmission periods. Many other forms of coupling networks, both inductive and capacitive or a combination of both, may be employed in lieu of those shown in Figs. l and 2 for utilizing the rectifier It! as an uncoupling device.

The above described type of transmit-receive switching device has the advantage that it consumes very little power,even'at high frequencies, and therefore is admirably suited for use in lowpower transmitter-receivers, particularly those of the portable, batteryoperated type. Its action is-practically instantaneous, and it does not require any special keep-alive voltage source as do many of the'transmit-receive switches now available. The bias-voltage source 34 may be the same source as that which supplies current to the filaments as'za and 50 of the tubes in the receiver and transmitter. The switch furthermore has no moving parts and does not require any adjustments. The transmitter operates very efficiently with this arrangement, and the receiver is well protected from over-loads.

While there has been disclosed What is" at present considered to be the preferred embodiment of the invention, it will be understood that various modifications thereof may be made within the true spirit-and scope of the invention as set forth in the appended claims.

-I claim:

1. In-a radio transmitter-receiver system, the combination including acommon antenna cir cuit, an input circui-t for applying signals-to'the receiver portion of said system and including a high-Q inductancecoil coupledtosaid antenna circuit, a metallic-oxide rectifier shuntedacross said inductancecoil in-sai-d receiver input circuit presenting negligible capacitance to said input circuit, biasing means coupled-tosaid rectifier to render said rectifier non-conductive -to signals below* a selected threshold so that optimum coupling between said input circuit" and said antenna circuitis maintained for such signals,-an' output circuit for the transmitter portion of said systemyahigh-Q inductance coil included'insaid outputcircuit and coupled to said antenna circuit and to said receiver-input circuit'and supplying asignal to-the latter circuit exceeding theaforesaid-threshold to render said rectifier conductive-and place a low resist-- ance shunt across said inductance coil in said receiver input circuit reducing the-Q thereof: and

decoupling said input circuit fromthe output circuit .of said transmitter and from said antenna circuit.

2. In a radio transmitter-receiversystem, the combination including a common antenna-circuit, an input Tcircuit for applying signals to the "receiver portioh ofsaid system and includinga high-Qinductance coil coupledto said antenna circuit and having-one side connected toa point of reference potential, 'a metallic-oxide rectifier and a-sourceof bias potential connected inseries across said inductance coil in said receiver input circuit and presenting negligible'capacitance to .said' input circuit, said bias sourcerenderlng said rectifier non-conductive to" signals-.b'elow a selected threshold so that optimum coupling tion of -said rectifierand'said source to said point of reference potential; an output circuit for the transmitter-portion' ofsaid systempa high-Q inductance icoil incl-uded' in said output References Cited in the file or this patent UNITED STATES PATENTS Name Date Brown Aug. 16, 1932 Number Number 0 Number Name Date Frink Aug. 14, 1934 Dietrich Jan. 24, 1939 Patterson Dec. 3, 1946 Benware Jan. '7', 1947 Atkins Sept. 2, 1947 Keister Mar. 23, 1948 Ransley Apr. 6, 1948 FOREIGN PATENTS Country Date Germany Nov. 14, 1908 

